One of the important things in colon carcinogenesis has been known to be point mutation of ras oncogene and about 11 kinds of mutation on codon 12, 13 and 61 of k-ras or N-ras oncogene are reported by several investigators. In vertebrates, point
mutation has been detected in chemical carcinogen induced cancers.
Ras oncogene encoded protein produce p21 has been known to regulate cell proliferation and differentiation by p21-GTP or GDT complex with point mutation. Investigators reported that p21 protein stimulated malignant transformation and its
expression
was
changed by development and progress of cancers.
To investigate the incidence of point mutation codon 12, 13 of c-K-ras oncogene in DMH-induced colon cancers and p21 protein products expression encoded by v-k-ras or v-H-ras oncogene according to exposure time of carcinogen and cell
differentiation,
authors divided 90 experimental animals into control(30) and experimental(60) groups, Each group was divided into three groups by sacrificing time after subcutaneous injection of 20mg of DMH or lml of EDTA weekly for 20 weeks; group I(20 weeks),
II(26
weeks) and III(32 weeks).
Point mutations were detected by paired-PCR with mutation-specific primers and agarose gel electrophoresis in 23 colon cancer tissues and p21 protein product expressions were investigated by immunoperoxdase staining using mouse monoclonal IgG
antibody
against v-K-ras and v-H-ras endcoded p21 protein product as primary antibdoy and avidin-tiotin complex.
@ES The results were obtained as follows:
@EN 1) The incidences of DMH-induced colon cancer were 30% in group I and II, 55% in group III, Overall 27 cases( 23 animals) of colon cancers wre observed. But only on colon cancer and 23% of polyps were detected in control groups.
Histopathologically
51.5% of well differentiated, 37% of moderately differentiated and 11.1% of poorly or mucinous adenocarcinomas were observed.
2) The indences of point mutation of 23 colon cancers were 34% of GAT, 17% of TGT, 17% of GTT mutation on codon 12 and 30% of GAC mutation with overall 78% of mutations. But no mutation was observed in normal colon tissues.
3) The expression of p21 protein products of v-K-ras in DMH induced colon cancers was 74% of positive which is consisted of 11% A-type, 55% of C-type and 7% of S-type in 27 colon cancer tissues. C-type was gradually increased from 17% of group I
to 25%
of group II and 92% of group III, while F-type was changed from 17% of group I to 25% of group II and 0% of group C. Simillary the expression of V-H-ras was 74% of positive which is consisted of 11% of A-type, 59% of C-type and 4% of S-type in
overall.
C-type was incresed from 17% of group I to 37% of group II and 92% of group III.
Positive expression was gradually increased from 33%(group I) to 62%(group II) and 100%(group II) in both v-K-ras and v-H-ras.
4) The positive p21 expressions for v-K-ras and v-H-ras were 69% and 77% in well differentiation and, 90% and 80% in moderately differentiated carcinomas. With above results, authors considered that point mutation of c-K-ras oncogene play an
important
role in DMH induced colon carcinogenesis. Expression of p21 protein product is increased by increasing DMH exposure time and differentiation which may be used in early detection and prediction of prognosis of colon cancers.
|